Chronic kidney disease (CKD) is a progressive loss of kidney function leading to kidney failure. Despite treatment of CKD with renoprotective agents, there is no therapy that slows or halts disease progression. Hallmarks of CKD are tubulointerstitial (TI) fibrosis, tubular atrophy, and inflammatory cell infiltration. Proximal tubules cells contribute to TI fibrosis and to the pathogenesis of CKD by promoting pro-inflammatory cytokines and extracellular matrix production, as well as myofibroblast differentiation of surrounding fibroblasts. The discoidin domain receptor 1 (DDR1) is a matrix receptor that is activated by collagen, upregulated in proximal tubules of injured kidneys and a positive regulator of collagen synthesis. Moreover, DDR1 induces the secretion of inflammatory cytokines and TGF-? that induces myofibroblast differentiation. Using a mouse model of severe acute kidney injury (AKI) that progresses to CKD, we showed that DDR1KO mice have reduced acute tubular injury and long-term post injury fibrosis. This protection is accompanied by decreased proximal tubule damage, macrophage infiltration, deposition of TI collagen, and ?SMA positive cells. In proximal tubule cells, DDR1 promotes synthesis of collagen, activation of pro-fibrotic intracellular signaling, and secretion of pro-inflammatory cytokines and TGF-?. Thus, DDR1 plays a deleterious role in the development of TI fibrosis making it a promising therapeutic target. Based on these findings, we hypothesize that upregulation of DDR1 on proximal tubule cells contributes to TI fibrosis by activating pro-fibrotic pathways and promoting secretion of pro-inflammatory and pro-fibrotic cytokines. Aim 1 will determine the contribution of DDR1 on proximal tubule cells to TI fibrosis. We hypothesize that DDR1 is a critical modulator of TI fibrosis that regulates pro-fibrotic and pro-inflammatory signaling in proximal tubule cells. We will induce severe AKI that progresses to CKD in DD1KO mice and newly generated TSH- DDR1 transgenic mice in which the TetO7-CMV promoter drives expression of a DDR1 shRNA capable of inhibiting DDR1 expression in the presence of a cell specific reverse tetracycline transactivator. To confirm that DDR1 contributes to TI fibrosis, we will treat mice with selective DDR1 inhibitors and follow injury over time. Aim 2 will determine the mechanisms whereby DDR1 contributes to TI fibrosis. Based on evidence that DDR1 promotes the phosphorylation of pro-fibrotic and pro-inflammatory transcription factors (canonical signaling) and it translocates to the nucleus where it interacts with chromatin and the RNA polymerase subunit RBP6, we will perform in vitro studies to test the hypothesis that DDR1 regulates gene transcription by activating canonical intracellular signaling as well as by acting as a transcription co-factor. This study will 1) generate novel insights into the molecular basis whereby DDR1 contributes to TI fibrosis and CKD; and 2) assess whether inhibition of DDR1 is beneficial in kidney injury. Our work could provide a novel therapeutic approach for the treatment and prevention of CKD.